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I have a dedicated server with a public ip running postfix with multiple domains. The emails are coming in all right but when I try to send mails from this machine they often get bounced back by external email servers with this error message:

"refused to talk to me: 501 HELO no reverse dns name"

When I go to the domain's control panel (gandi.net) they don't allow me to setup a PTR record for my server. What can I do?

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    Contact the hostmaster at your hosting provider. They should be able to update the PTR record for the IP address they've allocated for your server. – Mathias R. Jessen Mar 28 '14 at 9:38
  • So contact the operator of the dedicated server hosting? What if they refuse to do it? Is there other way to go then? – Dota Mar 28 '14 at 9:57
  • Yes. This is an important and easy part of hosting servers. If a provider doesn't do it, you should not be doing business with them. – Michael Hampton Mar 28 '14 at 16:39
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Contact the hostmaster at your hosting provider. They should be able to update the PTR record for the IP address they've allocated for your server.

Most providers I've worked with or heard of will gladly help out with this.
Some might be so impudent as to ask for a fee, depending on your existing service level.

In some cases they might refuse to change the PTR value to your mailserver FQDN, because they themselves use it for asset tracking (you would see a long possibly nonsensical value like host123.dedicated.dc01.dota.customers.hostingprovider.tld or so)

If this is the case, simply change your mailservers HELO FQDN to what ever the PTR resolves to.
I believe you can control this using the smtpd_banner variable in your postfix configuration.
Simply change $myhostname (or whatever is in there) to host123.dedicated.dc01.dota.customers.hostingprovider.tld and the Reverse DNS checks will no longer fail

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rDNS demonstrates some competence on the part of the email server admin, and usually some degree of trust by at least one other admin. PTR records are controlled by the administrator providing the IP address, in this case the hosting provider. The A and MX records demonstrate trust of the administrator in charge of the domain's DNS, in this case you. With few exceptions, legitimate servers pass, but most spambots fail.

If you can't get the correct PTR and A records put in place to pass rDNS validation, use your provider's email relay server to send email. It is unusual for relay servers to have DNS issues. You can still use your own server as your MX as it does not require rDNS.

While you are updating your DNS, consider adding an SPF policy record if you don't have one. Given this current state of validation software add it as as TXT record, and if possible as an SPF record. SPF policies for domains which won't be used for email such as www.example.com are also recommended.

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